Friction couplings for the range of application mentioned here have torque control purposes, i.e. more particularly they serve to control the distribution of torque at two wheels of a driven axle or between two drivable axles. To be able to carry out suitable control processes, the coupling moment transmitted by the coupling has to be known, i.e. it has to be constantly determined by suitable means. In prior art processes of for determining the coupling moment, the values such as speeds, temperatures etc. are measured by sensors, theoretical values (transmission ratios, efficiency etc.) are calculated, and corrected factors (friction coefficients, efficiency, temperature and speed dependencies etc.) as determined by tests are stored. The measured, calculated and interpolated values are evaluated in a computer or processor unit and the correct current for achieving a calculated coupling moment is set at the electric motor of the actuator. There is thus provided an open loop.
Because of existing non-linearities and deviations in the coupling behavior and in the behavior of the actuator, the coupling moment values set in this way and thus the respective torque values at the wheel or axles in some cases greatly deviate from the theoretical physical values. The degree of accuracy achieved in this way for setting the coupling moment is sometimes not sufficient. Storing the required evaluation tables in an Electronic Control Unit (ECU) or in a processor is complicated and does not allow the complete physical model of the coupling to be copied sufficiently accurately. For evaluating the measured, calculated and interpolated values ECU storage and computer capacity are used and are time-consuming. Several sensors are required for obtaining the required measured values (speed measurements, temperature sensors, etc.).